Removal of ferric iron as hematite at atmospheric pressure
A process for the removal of ferric iron as hematite from a nickel solution containing ferric and ferrous ions including the steps of: raising the temperature of the nickel solution to between 90° C. and the boiling point of the solution at atmospheric pressure; raising the pH of the nickel solution to be between 2 and 3; and adding a hematite seed to facilitate hematite precipitation, wherein ferric ions are precipitated as hematite in a predominantly crystalline form.
1. A process for the removal of ferric iron as hematite from a nickel solution containing ferric and ferrous ions including the sequential steps of:
(i) raising the temperature of the nickel solution to between about 90° C. and the boiling point of the nickel solution at atmospheric pressure;
(ii) adjusting the pH of the nickel solution to be between about 2 and about 3; and
(iii) adding a hematite seed to precipitate ferric ions as hematite in a predominantly crystalline form and to form a solution substantially free of ferric ions;
(iv) recovering nickel from the solution substantially free of ferric ions, in an ion exchange step, to produce a nickel concentrated ion exchange eluate, and an ion exchange raffinate containing cobalt, ferrous ions, chromium, aluminum, manganese, and magnesium;
(v) thereafter, removing ferrous ions from the raffinate of the ion exchange step by:
(a) oxidizing ferrous ions to ferric ions by sparging the raffinate with air, oxygen or an air/oxygen mixture;
(b) raising the temperature of the raffinate to be between about 40° C. and the boiling point;
(c) adjusting the pH of the raffinate to between about 2 and about 3; and
(d) adding a hematite seed to precipitate ferric ions as hematite in a predominantly crystalline form to form a slurry.
2. The process according to claim 1 wherein nickel is recovered in the ion exchange step using a continuous ion exchange device.
3. The process according to claim 1 wherein step (v)(b) comprises raising the temperature of the raffinate to be between 50° C. and 80° C.
4. The process according to claim 1 wherein step (ii) comprises adding a neutralizing agent to the nickel solution.
5. The process according to claim 4 wherein the neutralizing agent is limestone or saprolite.
6. The process according to claim 5 wherein saprolite is used as the neutralizing agent and the hematite seed used in step (iii) is added at a dose of at least a weight ratio of 1:1 to the added saprolite.
7. The process according to claim 5 wherein saprolite is used as the neutralizing agent and the hematite seed used in step (iii) is added at a dose of at least a weight ratio of 3:1 to the added saprolite.
8. The process according to claim 5 wherein limestone is used as the neutralizing agent and the hematite seed used in step (iii) is added at a dose by weight of 1:1 to 3:1 to the hematite formed during the precipitation of ferric ions as hematite in a predominantly crystalline form.
9. The process according to claim 8 wherein the limestone dose added is in a ratio of 1:1 to 1:1.3 of the stoichiometric weight of the ferric ions precipitated during the precipitation of ferric ions as hematite in a predominantly crystalline form.
10. The process according to claim 1 wherein the ion exchange step uses an ion exchange resin selected from a bis-picolylamine chelating resin or an iminodiacetate chelating resin.
11. The process according to claim 1 wherein cobalt is recovered from the ion exchange raffinate in a consecutive solvent exchange step with an organic reagent that includes a phosphinic acid.
12. The process according to claim 1 wherein the hematite seed used in step (v)(d) is added at a dose of at least a weight ratio of 1:1 to applied saprolite.
13. The process according to claim 12 wherein the hematite seed used in step (v)(d) is added at a dose of at least a weight ratio of 3:1 to applied saprolite.
14. The process according to claim 1 wherein the portion of the hematite containing slurry is returned to the nickel solution to act as a continuous hematite seed.
15. The process according to claim 1 wherein the pH of the slurry is raised to 6 with the addition of lime to precipitate out aluminum, chromium and some manganese, while any remaining ferric or ferrous iron will precipitate as hematite and/or magnetite.
16. The process according to claim 15 , wherein the slurry undergoes a solid/liquid separation step to remove hematite and/or magnetite in a predominantly crystalline form, leaving a solution containing cobalt, magnesium and manganese.
17. The process according to claim 16 wherein cobalt is recovered from the solid/liquid separation step by either ion exchange or solvent extraction.
18. The process according to claim 17 wherein cobalt is recovered by a solvent extraction using step using an organic reagent that includes a phosphinic acid.
19. The process according to claim 17 wherein cobalt is recovered by an ion exchange step with a resin selected from the group consisting of a bis-picolylamine chelating resin and iminodiacetate chelating resin.
20. The process according to claim 19 wherein cobalt is recovered by an ion exchange step with a continuous ion exchange device.